ADSORPTION OF TIN ON THE GE(111)-C(2X8) SURFACE STUDIED WITH SCANNING-TUNNELING-MICROSCOPY AND PHOTOELECTRON-SPECTROSCOPY

The growth and epitaxy of Sn on Ge(111) have been investigated using scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and core level photoelectron spectroscopy for coverages ranging from 0.4 monolayers (ML) to above the critical coverage at 1.6 ML. At the lowest coverage a (root 3 X root 3)R30 degrees reconstruction is formed at an annealing temperature of 250-300 degrees C while an annealing above 500 degrees C creates a dimer-adatom-stacking fault (DAS) (7 X 7) structure. In the (7 X 7) structure we argue that Sn occupies both adatom and dimer sites. A previously suggested difference in the (root 3 X root 3)R30 degrees reconstruction at different coverages could not be revealed in our STM images and it seems likely that the structure is the same both at 0.4 and 0.7 ML Sn coverage. We also report the observation of a new superstructure, a (4 X root 7) reconstruction in the submonolayer regime, which appears as a minority structure in disordered regions adjacent to a (5 X 5) DAS structure, Finally in the post-monolayer region a (3 X 2 root 3) structure, surrounded by vast areas of an amorphous tin overlayer, has been imaged by STM. As the coverage was increased, the amorphous layer completely covered the ordered (3 X 2 root 3) phase, which still could be observed in LEED. Additional room temperature deposition of Sn deteriorated the fractional order LEED spots presumably due to indiffusion of Sn from the interface as the critical coverage was surpassed.